Hydraulically-controlled transmission assemblies are an efficient way of controlling the speed and direction of land vehicles, such as walk behind and ride-on lawnmowers, ATV, and tractors.
Some known hydraulically-controlled transmission assemblies include high reduction mechanical gearing that can compromise the relative smoothness of the control of the vehicle. In addition, these transmission assemblies may be inherently limited in the amount of ground engaging power, and thus unable to put more than a limited amount of the engine's horsepower into ground engaging tasks. This affects control, accuracy and longevity of the transaxle as well as compromising the vehicle's performance and otherwise limiting the vehicles applications.
Another known hydraulically controlled transmission assembly includes a gerotor motor of the type having a spool valve that connects to a main output drive shaft. The output end of the main output drive shaft is disposed on one side of the rotor assembly and the spool valve and brake assembly are disposed on an opposite side of the gerotor assembly. Such a configuration requires complicated attachment of the spool valve to the main output drive shaft and a portion of the main output drive shaft orbits and rotates. Furthermore, the spool valve includes an extension to which brake disks are attached, thus requiring a larger housing assembly for the hydraulic device.
Other known hydraulically-controlled transmission assemblies, which include a hydraulic motor and a brake assembly, typically comprise large housings and/or complicated drive connections and/or complicated fluid paths. Still other known ground engaging transaxles are substantial in design and weight.
Piston-powered pumped units, while adaptable, have their own requirements and restrictions including the need for separate motors or the need of an associated gear transmission to apply power to the ground. While these known drive systems are functional, their compromise in cost and performance of each design is apparent.